The pyruvate dehydrogenase complex (PDC) catalyzes the formation of acetyl-S-CoA

Question

The pyruvate dehydrogenase complex (PDC) catalyzes the formation of acetyl-S-CoA, which enters the Krebs (TCA) cycle. PDC has an intricate quaternary structure because it has several copies of each enzyme component. PDC is also considered to be the largest multienzyme complex in eukaryotes. A) Which are the three enzymes present in PDC? (They are abbreviated E1, E2 and E3... not very imaginative, right?) B) What is the stoichiometry of the PDC subunits in mammalian cells? (In other words, how many subunits each are there of E1, E2 and E3? C) How does the PDC connect glycolysis with the TCA cycle? D) Briefly compare and contrast pyruvate dehydrogenase with -ketoglutarate dehydrogenase (- KGD) complex (step 4 in Krebs cycle). Please note: You will find that -ketoglutarate is also called 2-oxoglutarate. E) Where are PDC and -KGD located?

Explanation / Answer

(A): The three enzymes present in pyruvate dehydrogenase complex (PDC) are

1. pyruvate dehydrogenase (E1)

2. dihydrolipoyl transacetylase (E2)

3.dihydrolipoyl dehydrogenase (E3)

(B): In mammalian cells pyruvate dehydrogenase (E1) has 30 subunits, dihydrolipoyl transacetylase (E2) has 60 subunits and dihydrolipoyl dehydrogenase (E3) has12 subunits.

(C): PDC complex catalyzes the conversion of pyruvate formed in glycosis to Acetyl-CoA  by a process called pyruvate decarboxylation. Now Acetyl-CoA enters TCA cycle for oxidation to generate energy.

(D): Both  pyruvate dehydrogenase complex (PDC) and -ketoglutarate dehydrogenase (- KGD) complex contains three different enzymes named E1, E2 and E3.

Enzymes present in PDC are pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2) and dihydrolipoyl dehydrogenase (E3).

Enzymes present in - KGD are oxoglutarate dehydrogenase (E1), dihydrolipoyl succinyltransferase (E2) and dihydrolipoyl dehydrogenase (E3).

Hence the 3rd enzyme dihydrolipoyl dehydrogenase (E3) is common to both PDC and - KGD complex.

Also the subunits of both the complex have similar structure.

(E): Both PDC complex and -KGD complex is located in mitochondria.

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